You might just as well buy another set from DX then you'll have spare everything, surely by the time you add shipping from somewhere else just for a battery pack it will be the same anyway, and I think you're more likely to get customs poking their nose in with stuff from the USA?
Oh, and if you connect 2 batteries via a Y cable to one lamp aren't you doubling the voltage and risking something blowing, 1 battery (for eg.) gives 5 volts so 2 would give 10v ?? Correct me if I'm wrong ❓ I'm no electrician? … Isn't there a laptop battery or something that would put out the correct voltage with a longer output that could be fitted with the correct fittings??